Engine Air Compressor?

[BrentD]

I am thinking you will need about 5 HP, CCW rotation electric motor. Here is a 30 cfm compressor.

Rotation shouldn't be a problem. If I need the motor to go the other way I can just turn it around. That's one reason I was planning on belt driving the whole thing.

As far as the drive train versus check valve thing goes, I'll probably just play around with it and see which way works best. If I end up keeping the coolant circulation system intact the extra complexity of the valve train isn't going to add all that much more. Of course after thinking about this a little more and reading about the timings, etc I may just be better off to use the check valves and lock all the engine valves closed. Would probably get better airflow that way sine the valves would be pressure operated rather than mechanical.

 

[BrentD]

Have you considered a PTO aircompressor?

What kind of work do you do that requires 30 cfm.?

This air compressor would be at my little workshop in town and I don't even have a riding lawnmower at the house in town so PTO isn't an option. My tractors and dozer are out on my families 50 acres 10 miles out of town.

I don't really know that I have anything that requires 30CFM. the 30CFM figure was just a guesstimate of what a compressor like this might be capable of. The biggest air hog I've got right now is my 40pound pressurized sandblaster. It really taxes my little 20-gallon 110V air compressor. The pump never cuts off.

I do, however have another application where I might need a high-CFM compressor. I work with the local crime-stoppers program on a Haunted House every October. We have a LOT of air operated props and the 75Gallon 4-horse, $1400 compressor we've got can barely keep up. We had to rig a squirrel-cage fan above it to keep it from overheating. If I could build something that could supplement or replace the big one and only spend a couple hundred dollars on it, it might save us some major headaches in the future.

 

[Iplayfarmer]

Ok, mabye I dont understand all I know about whats trying to be done (that has happened in the past). But aren't you going to need at least the intake valve functional to let air in the chamber to be compressed?

You're right. My bad.

You could probably make the engine air intake valve into a one-way valve by putting a softer spring on it.

 

[BrentD]

You could probably make the engine air intake valve into a one-way valve by putting a softer spring on it.

That's another excellent idea.

 

[Egon]

to need at least the intake valve functional to let air in the chamber to be compressed?

Not necessarily. With an intake and exhaust air valve running of the spark plug hole you do not need the engine valves functioning but they must be closed or the port sealed off.

 

[RWolf]

Considering my Air Compressor 40gal. uses a 5HP motor (probably rated peak) I think you are going to need roughly 10 - 15 HP motor minimum to run it. Sounds like an interesting project but I think the cost is going to build up so much that it would be cheaper to get another compressor and parallel it to the one you have for you haunted house.

 

[Iplayfarmer]

Considering my Air Compressor 40gal. uses a 5HP motor (probably rated peak) I think you are going to need roughly 10 - 15 HP motor minimum to run it. Sounds like an interesting project but I think the cost is going to build up so much that it would be cheaper to get another compressor and parallel it to the one you have for you haunted house.

I'm with RWolf on this one. I think you're going to need a lot of motor to run your little 3 cyl. engine.

If you don't already have the engine, I'd suggest looking onto a small import V-6. You could probably pick up a single V-6 for almost as cheap as a Geo engine, and then you could do the conversion so half the cylinders pump and the other half power. All the same principles would apply.

It would be really nice if you could have one side do the powering and one side do the pumping. This would simplify negotiating the exhaust and intake manifolds, etc.

 

[Brad_Blazer]

I've been running one of these for about 3 years now with the RPM derated to run off a 3hp motor.
Harbor Freight Tools - Quality Tools at the Lowest Prices
Works great.

If you have identical pool pump motors you might be able to put one on each side of the pump to drive the 2-groove pulley. The price does add up quickly when you start buying the pressure switch, check valves, fittings, etc. let alone the tank. You'll do well to get 3cfm per horsepower at 90PSI.

 

[BrentD]

I've been running one of these for about 3 years now with the RPM derated to run off a 3hp motor.
Harbor Freight Tools - Quality Tools at the Lowest Prices
Works great.

If you have identical pool pump motors you might be able to put one on each side of the pump to drive the 2-groove pulley. The price does add up quickly when you start buying the pressure switch, check valves, fittings, etc. let alone the tank. You'll do well to get 3cfm per horsepower at 90PSI.

Interesting... I know that the pool pumps I have are definitely identical. It might be possible to have them all working together to tun the machine, although that would be one weird pulley system.

 

[bobodu]

Ten horse electric..
Fifteen horse gas...
THOSE POOL PUMPS JUST AIN'T GONNA CUT IT.....
You're trying to build 100 psi from a single stage pump and that takes POWER.
If you go with gas,figure in some big money for the unloader,pilot valve and throttle control too. The smallest compressor we have at the plant is a five horse.When you go big,you're talking three phase or very expensive 220 volt single phase motors.
I built a compressor for my shop from a free pump,60 gallon tank and pneumatic cylinders I got for the scrap pile at work. I tried several engines I had and none of them were worth squat so I bought a clone from Harbor Freight. Broke the starter rope three times before I realized that I was trying to turn the pump too even though the unloader was open. I had to fab up a screw device to slip the belt just to roll the engine fast enough to even start it.

 

[Egon]

You could probably make the engine air intake valve into a one-way valve by putting a softer spring on it.

There was a time some of the old engines had intake valves that operated in that fashion.

 

[Iplayfarmer]

...You're trying to build 100 psi from a single stage pump and that takes POWER...

Okay, here's a brainstorm: What if you make your engine into a two stage pump? Pull ambient air into two of the cylinders, and have those two cylinders exhaust into the third. The third pulls in the partially compressed air and compresses it further. You'd probably need some kind of small surge tank (<1 gal.) inbetween unless you could time the two first stage cylinders to both be exhausting at the same time the third is sucking air in.

Would this be any better?

 

[Egon]

Usually when compression is staged the cylinder volume changes and inter coolers with fluid drains may be required.

 

[slowzuki]

Would have loved too but the car was hard against a wall and another car. I had to take the siding off the building to even get the air chuck onto the two of the valves.

Just a friendly suggestion... Next time you might consider taking the tires off and hauling them to the air instead of the whole car.

 

[Iplayfarmer]

Would have loved too but the car was hard against a wall and another car. I had to take the siding off the building to even get the air chuck onto the two of the valves.

I should have known it would be something like that.

 

[bobodu]

Usually when compression is staged the cylinder volume changes and inter coolers with fluid drains may be required.

Yep....the higher compression (secondary) cylinder would have to contain less volume (smaller). This could be accomplished by having two cylinders dumping into one but the would probably require a different crank.

 

[Iplayfarmer]

Yep....the higher compression (secondary) cylinder would have to contain less volume (smaller). This could be accomplished by having two cylinders dumping into one but the would probably require a different crank.

Do you think it could be done with a small surge tank?

 

[Redneck in training]

Okay, here's a brainstorm: What if you make your engine into a two stage pump? Pull ambient air into two of the cylinders, and have those two cylinders exhaust into the third. The third pulls in the partially compressed air and compresses it further. You'd probably need some kind of small surge tank (<1 gal.) inbetween unless you could time the two first stage cylinders to both be exhausting at the same time the third is sucking air in.

Would this be any better?

It would work but not as well as you might think. If the compression ratio is 8:1 then the second stage will have to be much smaller than half of the first stage. It will also require substantial intercooler.
To overcome this the compression ratio of the first stage would have to be lowered. To lower compression ration of the 1st stage is actually quite easy to do. You just need to increase so-called "dead space" by placing discharge valve certain distance from the head. Lower ratio of the first stage will also lessen demand for intercooling.

 

[Egon]

unloaders.

 

[Iplayfarmer]

It would work but not as well as you might think. If the compression ratio is 8:1 then the second stage will have to be much smaller than half of the first stage. It will also require substantial intercooler.
To overcome this the compression ratio of the first stage would have to be lowered. To lower compression ration of the 1st stage is actually quite easy to do. You just need to increase so-called "dead space" by placing discharge valve certain distance from the head. Lower ratio of the first stage will also lessen demand for intercooling.

I guess one of the things I'm shooting for is to lower the power consumption. I was guessing that if each of the pistons were only compressing the air halfway (i.e pistons 1 and 2 are taking it from 0 to 50 psi and piston 3 is taking it from 50 to 100) it would lower the power consumption. It would also lower the output, but it seems pretty well accepted amongst us that for the task at hand this setup would be more than sufficient.

By increasing the dead space to change the compression ratio like you suggest would it also decrease the amount of heat created? Even if it didn't would the heat created be more that normal operating temperatures of an engine. You'd have the radiator and engine cooling system there that could be used to cool.